Oil return system for refrigeration apparatus

ABSTRACT

Apparatus for assuring return of oil separated from refrigerant in a vapor cycle refrigeration system. Means are provided for positively effecting flow of oil from a lower pressure reservoir into a crankcase of a compressor which is normally maintained at a higher pressure. Such means may take the form of an eductor powered by flow of lubricating oil in a closed circuit with respect to the compressor.

United States Patent 1 1 Muench 1 1 Dec. 11, 1973 1 41 OIL RETURN SYSTEMFOR 2,4 8, 4/1947 Zwiclrl 1. 62/470 REFRIGERATON APPARATUS 2,892,3206/1959 Quick 62/471 2,975,613 3/1961 Heid0rr1.... 62/471 Inventor PaulMuench, Medford Lakes, 3,304,697 2/1967 Ramsey 62/471 NJ. 3,360,9581/1968 Miner 62/470 [73] Assignee: Borg-Warner Corporation, Chicago, 1

11L Primary Examiner-Meyer Perlin Attorney-Donald W. Banner et al. [22]Filed: Mar. 13, 1972 [21] Appl. No.2 233,895 [57] ABSTRACT Apparatus forassuring return of oil separated from re- [52] US. Cl. 62/470, 62/192frigerant in a vapor cycle r geration system. Means [51] Int. Cl. F25b43/02 are provided for p e y e fect ng flo of oil from a [58] Field ofSearch 62/84, 192, 193, lower pressure reservoir into a crankcase of a62/194, 470, 471, 472, 473 pressor which is normally maintained at ahigher pressure. Such means may take the form of an eductor [56] RefereCit d powered by flow of lubricating oil in a closed circuit UNITEDSTATES PATENTS with respect to the compressor. 1,899,378 2/1933 Zouck62/471 2 Claims, 1 Drawing Figure CONDENSER EVAPORATOR COMPRESSOR 52 on.STILL 5o SIGHT GLASS COM PR E550 Q BACKGROUND AND SUMMARY OF THEINVENTION Thisinvention relates to an oil return system forrefrigeration apparatus.

In vapor cycle refrigeration systems, refrigerants pro cess considerableaffinity for lubricant oil used in com- A pressors of such systems, sothat mixtures of the oil and refrigerants occur. Since lubricating oildestroys the high operating efficiency of the evaporator, itis mostdesirable to recover the oil circulating with the refrigerant leavingthe compressor and return it to the com- I pressor crankcase. Forthispurpose, an oil separator is used to protectthe compressor fromliquidrefrigerant and/or oil returninginquantity through the suctionline to the compressoriThe oil separator operates to separaterefrigerant from the oil, the oil being transferred to an oil receiver,which may also be a still, for return to the compressor crankcase.Whenthe pressure of the oilinthe crankcase is higher than the pressureof the oil in the oil receiver, it is necessary to employ means totransfer the oil to the higher pressure chamber. While a mechanical pumpcan beused to perform this function, the pump has a multiplicity ofmoving parts subject to wear and deterioration, in addition to requiringan electrical or other source of motive power necessitating controls forits correct operation. While other liquid transfer means have beensuggested, such means have been found to be incapable of transferringtheoil if considerablepressure differences exist between the oilreceiver and the compressor crankcase.

The present invention contemplates an oil return system featuring means,suchas an eductor, designed to be powered by main oil pressure from thecompressor lubricating system and topositively effect flow of oil from alower pressure reservoir into a compressor crankcase which is normallymaintained at a higher pressure.

It is an object of the invention to provide an improved oil returnsystem for refrigeration apparatus.

Another object of the invention is to provide an improved oil returnsystem in which an eductor is disposed in a closed compressorlubricating oil circuit and powered by flow of oil therein to compelflow of oil from a reservoir into the circuit and thereby intothecompressor crankcase.

Additional objects and advantages will be apparent from the followingdetailed description taken in conjunction with the drawing.

DESCRIPTION OF THE DRAWING The single FIGURE is a schematic diagram of arefrigeration system utilizing the oil return system of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the FIGURE,there is shown a refrigeration system employing a pair of compressors operating in parallel to feed a single condenser and single evaporator,although various combinations of multiple condenser and evaporatorsystems, which are familiar to thoseskilled in the art, may be employed.Compressors and 12 dischargehot gas into respective outlet lines 14 and16 which are connected to a common hot gas discharge line 18. The gaspasses through an oil separator 20 of any common type and is deliveredthrough line 22 to condenser 24. Gas then flows through a re-..

striction, such as provided by a thermostatic valve or an orifice 26,into an evaporator 30, which iscommonly of the flooded type. The suctiongas, leaving the evaporator, is delivered to what is referred to as adead-end trap 32 which is adapted to eliminate any trace of oil carriedin the suction gas to prevent the same from flowing into the suctionside of the compressors. The suction gas passes through line 38 which isjoined to suction lines 40 and 42 of compressors 10 and 12,respectively.

Oil, separated from the discharge gas, is delivered by a line 44 to astill and receiver 50 where the refrigerant is boiled off and returnedto the suction side of the system preferably to trap 32 through line 54.At the same time, the oil, separated from the suction gas, is deliv eredto the still through line 56.

The refrigerant-free oil, which is collected in the still, is availablefor use in the compressors in the event the oil level in either one ofthem drops below a predetermined point.

The oil makeup system includes eductor 58 which, in effect, operates asa pump driven by oil circulating in line 60 and is responsive to thepressure generated by the oil circulating system in the compressor 10.In this way, the relatively low pressure oil in the still 50 and flowingin lines 62 and 64 is positively driven into the oil return system bybeing aspirated into the return stream by the eductor 58. In practice,the oil is continuously circulating through a pressure-responsive valve65 (sensing oil pressure through line 61) which has a minimum setting ofabout 100 psi and a maximum setting of 150 psi. When the oil level inthe compressor crankcase drops to a dangerous level, the oil level floatswitch 66 completes an electric circuit to activate a solenoid valve 68in line 64 to permit the oil in still 50 to enter the suction side ofthe eductor. When the oil level is brought up to the proper point, theswitch 66 will open to deenergize the solenoid of the valve 68 and valve68 closes to discontinue oil flow from still 50 to the eductor. The samemanner of operation applies to oil circulating line 71, pressure sensingline 73, eductor 70, pressure-responsive valve 72, oil level switch 76,and solenoid valve 74 on compressor 12. Check valves 69 and 75 areemployed to prevent back flow of oil from the compressor to the oilstill.

A feature of the invention resides in the use of oilsampling linedirectly connected to the evaporator 30 and to line 56which permits oilto flow into the still 50 via line '56 when an electric heater element82 and solenoid 84 of valve 86 are energized, valve 86 being opened byactivating solenoid 84. Solenoid 84 and electric heater element 82 maybe operatively interconnected by control line 90 so that they areenergized simultaneously by suitable means (not shown). This will assurethat the heater will be in operation to boil off refrigerant flowingfrom evaporator 30 through valve 86 to the oil still 50.

In the preferred embodiment of the invention, the oil return system canoperate with unequal compressor loadings or crankcase pressures; aminimumquantity of oil is in circulation through the oil still andreceiver; there is more positive draining of the dead-end trap 32;simplicity of piping and equalizing of the oil still isrealized; and thesystem is in operation at all times that the compressor is operating.

It will be apparent that, while this invention has been described inconnection with a refrigeration system employing dual compressorsoperating in parallel to supply a single condenser and evaporator, it isbelieved obvious the invention can be used in a refrigeration systememploying a single compressor. Also, the use of an oil still or oilreceiver is optional. Accordingly, it is to be understood that thedescribed preferred embodiment of the invention is by way ofillustration and not by way of limitation; and the scope of the appendedclaims should be construed as broadly as the prior art will permit.

What is claimed is: I

1. In a refrigeration system including a compressor having anoil-carrying crankcase; an oil separator connected to the high pressureside of said compressor to effect separation of oil from therefrigerant; means pro viding a closed lubricant oil circuit in fluidcommunication with said crankcase of said compressor; an oil receiverconnected to the oil discharge side of said oil separator and to saidcircuit, said receiver containing oil under pressure lower than thepressure of the oil in said crankcase; and eductor means in said circuitand operative, in response to the pressure generated by the oilcirculating in said circuit, to effect flow of oil from said receiverinto said circuit.

2. A refrigeration system as defined in claim 1 including a conduitconnecting said receiver to said closed lubricant oil circuit; means forsensing the oil level in'said crankcase; and valve means associated withsaid con duit and responsive to said oil level sensing means forpermitting oil in said receiver to flow through said conduit into saidcircuit by the operation of said eductor whenever said oil level is lessthan a predetermined value.

1. In a refrigeration system including a compressor having anoil-carrying crankcase; an oil separator connected to the high pressureside of said compressor to effect separation of oil from therefrigerant; means providing a closed lubricant oil circuit in fluidcommunication with said crankcase of said compressor; an oil receiverconnected to the oil discharge side of said oil separator and to saidcircuit, said receiver containing oil under pressure lower than thepressure of the oil in said crankcase; and eductor means in said circuitand operative, in response to the pressure generated by the oilcirculating in said circuit, to effect flow of oil from said receiverinto said circuit.
 2. A refrigeration system as defined in claim 1including a conduit connecting said receiver to said closed lubricantoil circuit; means for sensing the oil level in said crankcase; andvalve means associated with said conduit and responsive to said oillevel sensing means for permitting oil in said receiver to flow throughsaid conduit into said circuit by the operation of said eductor wheneversaid oil level is less than a predetermined value.